He was pretty specific about what battery he's talking about.
Unfortunately, only Seidio people have some kind of idea of its release date. It is probably taking longer due to the fact that they have to produce a new battery cover to come with it due to it's larger depth.
As far as battery life increase goes, there was a link somewhere showing that Seidio batteries yield about 85% the life it is advertised. Considering the fact that the stock battery is 1500mAh, you're looking at double the juice on a 3500mAh battery.